Scientists Build the World's Tiniest Rotary Motor

This new motor is so tiny even an HIV virus dwarfs it. A team of physicists led by Philip Ketterer of the Technical University of Munich have just built, molecule by molecule, the smallest rotary engine ever created by man.

Only 40 nanometers tall, the tiny device is made of three separate components that click together to form crude versions of an axle bearing and a spinning crank lever. Inspired by the flagella (whip-like propellers) used by many bacteria, the motor looks like a half a helicopter blade, and it creates forward thrust through the rotational motion of that blade. The new device is outlined in a paper published today in the journal Science Advances.

"It's a step toward the long-term goal of artificial nano-robots," says Ketterer. "You could easily imagine a future where similar such motors are used for propelling nano-robots in our bodies, much in the same way that bacteria naturally move about."

Ketterer's molecular motor is the latest advancement in a research field called multilayer DNA origami. Scientists use straps of physical DNA material, as if it were plywood or brick, to form various devices and machines. They're currently developing the nano-sized equivalents of all the tools you'd find in an engineer's toolbox, including hinges, clamps and bearings. Today's rotary motor, with an axle bearing case that clicks together, is easily "the most complex device made so far with this technique," Ketterer says.

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Why build this motor with DNA? "Well, this has nothing to do with DNA's primary role as data storage for genetic information," Ketterer says. Rather, the DNA molecules are both flexible and incredibly well understood from a materials perspective because so much research has happened in genetics. As a result, DNA makes "a great building material with some interesting physical properties," he says, "and we use chemically synthesized DNA, which you can get loads of for cheap."

For now, Ketterer himself actually refrains from calling this creation a "motor," because the device is powered passively. It creates rotational motion by harnessing the energy of the ambient, irregular collisions of molecules around it, also known as Brownian motion. Basically, it's powered by atomic collisions. This means that currently, the scientists can't flip these motors off and on, and they also can't control which way the rotors turn.

But Ketterer's team is now investigating different ways to power these motors and control their spin. One idea involves using laser light to transfer pulses of energy to the rotary motor via waves. However, Ketterer gets the most animated when he talks about the prospect of using a influx of energy-rich molecules, like ATP, to power his motors. This is the very process that bacteria and other cells use to power a whipping flagella.

"It's still a faraway goal, but when we have an [steady] energy source and can control the directional motion of these devices," Ketterer says—then we'll have a working engine for itty-bitty bots.

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